Communication systems are well known and comprise many types including land mobile radio, cellular radiotelephone, personal communication systems, and other communication systems. Within a communication system, transmissions are conducted between a transmitting device and a receiving device over a communication resource, commonly referred to as a communication channel. To date, the transmissions have typically consisted of voice signals. More recently, however, there has been rapidly growing interest in carrying other forms of signals, including high-speed packetized data signals, suitable for video, audio and other high bandwidth data applications. For ease of operation and to facilitate cost effective upgrading of existing voice systems to allow for data services, it is preferable to have the data transmission capability overlay the existing voice communication capability, such that its operation is essentially transparent to the voice communication system while still utilizing the communication resources and other infrastructure of the voice communication system.
One such communication system currently available with transparent data transmission capabilities is a General Packet Radio Service (GPRS) system, as described in the Global System for Mobile Communications (GSM) Technical Specification (TS) 08.18 and incorporated by reference herein. Within such a communication system, a GSM communication system is overlaid with a GPRS communication system. In contrast to GSM's service model, which offers telephony on demand, GPRS's service model offers a wireless Wide Area Network (WAN) supporting a wide range of applications such as low-volume intermittent telemetry, video, web browsing, and the transfer of large amounts of data.
In such a system, as the location of the remote unit (RU), RF conditions or congestion level deteriorate, and because the RU does not have knowledge of the congestion level of the source or neighbor cell, the remote unit (RU) may experience better radio conditions or congestion level from a neighboring cell. At that point, the GPRS network or the RU may perform a cell reselection. In GPRS networks, cell reselection may occur as often as every fifteen seconds. During cell reselection, the RU terminates the temporary block flow (TBF) from its current source cell and reestablishes the connection after a period of approximately two to three seconds at the neighboring target cell. During this period, the RU is unable to receive any downlink data and does not maintain any contact with the core network.
More particularly, during an auto downlink procedure, the network starts a new downlink TBF for the RU after the RU has requested an uplink TBF, and also currently does not have a downlink TBF active. Dummy downlink data is transmitted to the RU in this auto downlink TBF until either real downlink data is ready to transmit to the RU, or a timer expires. The network starts the auto downlink TBF once it knows the RU's RA-CAP information after the uplink TBF is established.
By way of example, in the case of a two-phase packet access, the network knows the RA-CAP information when it receives the Packet Resource Request (PRR) message from the RU. The RA-CAP information is embedded in the PRR message. In the case of a one-phase packet access, the network first must obtain the RU's identity. The identity of the RU is transmitted to the network in the first uplink data block. The first uplink data block contains the RU's Temporary Logical Link Identity Identity (TLLI). Once the network has the RU's TLLI, the network can retrieve the RU's RA-CAP information by executing an RA-CAP-UPDATE procedure. The RA-CAP-UPDATE procedure is used by the PCU to request an RU's radio access capabilities from the SGSN, as defined in GSM TS 08.18. The SGSN may or may not support this procedure. Hence, because of the messaging required between the network and the PCUs and other network components, the downlink data from the network is significantly delayed from reaching the remote unit each time cell reselection occurs.